1. Field of the Invention
The present invention relates to a lens surfacing assembly and a method for grinding and polishing glass or plastic optical lenses. The assembly is primarily intended for use with a rigid lapping tool having an arcuate surface that is configured generally to the shape of the finished lenses. The radius of curvature of the arcuate surface is reduced by a standard compensation that equals the thickness of an adhesive member plus a double sided surfacing pad or the thickness of the adhesive member plus a polishing cloth.
2. Description of the Prior Art
Pads with abrasive mediums thereon are well known in the art. U.S. Pat. No. 81,986, issued to J. H. Crane discloses a flexible abrader which comprises a central layer or web of flexible material that is surfaced on both faces with suitable abrading material. The patent to Holzhauer, U.S. Pat. No. 3,785,094, discloses a synthetic resin impregnated fiberglass man having a layer of abrasive grains attached to both surfaces of the mat.
A number of other U.S. patents; in particular, U.S. Pat. No. 3,144,737, issued to K. D. Faas; U.S. Pat. No. 3,959,935, issued to W. Stoppacher; U.S. Pat. No. 4,288,233, issued to R. C. Wiand; and U.S. Pat. No. 4,962,618, issued to S. J. Wylde, each disclose a single sided pad made from various materials, one side having an abrasive material and the opposing side an adhesive for attaching the pad to a lapping tool. U.S. Pat. No. 4,788,798, issued to DeFranco, et al., discloses a lens polishing pad having one side with an abrasive surface and the other side with a strippable adhesive for removable attachment to a lapping tool.
The current apparatus and process for rough grinding, fine grinding, and polishing optical lenses require three separate pads with adhesive attached thereto. Lapping tools are designed to have a predetermined radius of curvature so its radius of curvature plus the thickness of the coarse pad and the thickness of the finishing pad equal the final radius of curvature of the finished lens. This reduction in the standard lapping tool's radius of curvature is 0.018 inches and is called the standard compensation. The lapping tool, with the coarse pad attached, and a lens blank, having the appropriate radius of curvature cut therein, are mounted within a lens surfacing machine. The lens is roughly ground to a radius of curvature equaling the radius of curvature of the lapping tool plus the thickness of the lens surfacing pad. The curvature of the lens blank now differs substantially from the final desired curvature. The center of the lens is close to the final desired curvature, but the peripheral area of the lens has much material to be removed due to the shorter radius of curvature when only the coarse pad is attached to the lapping tool. A second lens surfacing pad with a finer abrasive is now attached to the lapping tool so that it overlies the existing coarse pad, and thus, increasing the radius of curvature by the additional thickness of the fine pad. This total radius is the desired radius for the finished optical lens. However, as the radius of the coarse pad is an incorrect radius, when the fine pad is used to grind the lens, the fine pad must not only remove the scratches caused by the coarse pad, the fine pad must also reconfigure the curvature of the lens to the final radius of curvature, requiring the removal of considerable material using a fine grit, particularly on the peripheral area of the lens. Removal of material is slower when accomplished by a fine pad versus a coarse pad. Now that the lens has been formed to the proper curvature, the polishing pad for the final polishing cannot be added on top of the other two grinding pads. The grinding pads must be removed from the lapping tool, the lapping tool cleaned, and a polishing pad of the appropriate thickness (the sum of the coarse and the fine grinding pads) must be attached to the lapping tool.
Considerable operating time is lost using the fining pad to re-conform the radius of curvature of the lens. Time is also lost during removal of the two grinding pads with the attached adhesive and during cleaning of the tool and application of new adhesive and the polishing pad. In addition, the pads having adhesive thereon are difficult to reuse as the adhesive on the pads may stick to itself damaging the pads.
It is clear then, that a method and apparatus are needed that will provide a means for reusing the grinding and polishing pads and which will reduce the time required for grinding the blanks to the final radius of curvature.